The field of the present invention is flashlights.
Flashlights of varying sizes and shapes are well-known in the art. In particular, certain of such known flashlights utilize two or more dry cell batteries, carried in series in a cylindrical tube serving as a handle for the flashlight, as a source of electrical energy. Typically, an electrical circuit is established from one electrode of the battery through a conductor to a switch, then through a conductor to one electrode of the lamp bulb. After passing through the filament of the lamp bulb, the electrical circuit emerges through a second electrode of the lamp bulb in electrical contact with a conductor, which in turn is in electrical contact with the flashlight housing. The flashlight housing provides an electrical conduction path to an electrical conductor, generally a spring element, in contact with the other electrode of the battery. Actuation of the switch to complete the electrical circuit enables electrical current to pass through the filament, thereby generating light which is typically focused by a reflector to form a beam of light.
The production of light from such flashlights has often been degraded by the quality of the reflector utilized and the optical characteristics of any lens interposed in the beam path. Moreover, intense light beams have often required the incorporation of as many as seven dry cell batteries in series, thus resulting in a flashlight having significant size and weight.
Efforts at improving such flashlights have primarily addressed the quality of the optical characteristics. The production of more highly reflective, well-defined reflectors, which may be incorporated within such flashlights, have been found to provide a more well-defined focus thereby enhancing the quality of the light beam produced. Additionally, several advances have been achieved in the light admitting characteristics of flashlight lamp bulbs.
Since there exists a wide variety of uses for hand-held flashlights, the development of the flashlight having a variable focus, which produces a beam of light having a variable dispersion, has been accomplished.
High quality flashlights are commonly sealed for protection from moisture and other harmful environmental elements. Proper sealing is most specifically achievable with machined metallic flashlights which employ nonpermeable materials and can be constructed with reliable sealed joints. Such flashlights which have variable focus through movement of the head toward and away from the flashlight barrel experience an expansion and contraction of the internal volume thereof which is unvented, resulting in internal pressure changes. Also as the temperature of the barrel changes, variation in pressure within the internal volume can also occur. These pressure changes are understood, at least theoretically, not to be substantial. However, in infrequent occurrences, pressure has built up in such devices. This is believed to be the result of outgassing from a defective battery.
Heretofore, flashlights have been known to include vent holes or simple imperfections in the manufacture which unintentionally create vent passages. Where moisture is considered to be a problem, such vent holes may include a moisture impervious diaphragm to allow the passage of air but not moisture into and out of the internal chamber of the flashlight. Such devices are believed to be less than optimum in that various harmful elements in gaseous form can be drawn into the internal volume of the flashlight. Further, such devices cannot resist substantial overpressure resulting from deep submersion or other equivalent conditions. The cross-sectional size of the passage can also result in problems with blockage.